Positive long-term effect of mulching on species and functional trait diversity in a nutrient-poor mountain meadow in Central Europe

Oligotrophic mountain meadows are threatened biodiversity hotspots throughout Europe. The traditional summer hay-making followed by autumn grazing is no longer economic and question is whether alternative managements can maintain both plant species and functional diversity typical of these habitats. In the Bohemian Forest Mts., we applied three treatments (mowing once a year - i.e., cutting and removing the biomass, mulching once a year - cutting and leaving the crushed biomass to decompose in situ, fallowing - no cutting) in order to assess temporal changes in meadow vegetation, plant trait composition and biomass production in a 13-year experiment. We recorded for each species twenty-five traits as to be most informative of plant strategies related to growth, resource acquisition and carbon-water economy. We compared different components of trait composition (community averages that mostly reflect traits of dominant species vs. the Rao index of functional diversity that reflects trait dissimilarity among species) and their impact on biomass production. We show that mulching promotes species and functional diversity by facilitating heliophilous forbs and legumes with more acquisitive strategies in resource use and release, e.g., higher foliar N and P content. This occurs at the expense of tall grasses (with resource-retentive strategies, e.g., high leaf dry matter content) which dominate the mown and fallow plots. The divergence in most quantitative traits indicates that niche complementarity is the dominant assembly process in mulched plots, which can prevent competitive exclusion and enable species coexistence. The divergent development was detected only after 5-6 years. This slow floristic and functional response is caused by acidity of soil and severe mountain climate that preclude rapid responses of vegetation to land-use changes. We conclude that mulching represents a good compromise maintaining both plant species and functional diversity as well as a relatively high biomass production. Mowing without grazing leads to gradual nutrient loss and thus reduces the productivity and diversity in these oligotrophic ecosystems. Fallowing causes gradual loss in diversity by increased grass competition and litter accumulation.     

基于郑州地铁下穿南水北调干渠的Peck公式反演分析

土压平衡盾构隧道下穿通水运行中的南水北调工程,在国内尚属首例.以郑州地铁城郊线土压平衡盾构隧道下穿南水北调中线干渠区间实测数据为依据,将Peck公式法运用于隧道下穿南水北调工程引起的地表沉降预测研究中,利用反演分析法,通过引入最大沉降量修正系数j和沉降槽宽度修正系数k,结合实测数据对Peck公式进行修正,得出适用于郑州...     

利用NDVI-Albedo反演厦门后溪流域地表特征

利用TM影像与6S模型反演获得精确NDVI与Albedo数据,在NDVI-Albedo散点图空间综合分析了后溪流域的植被和地表反照率空间分布特征。后溪流域整体上植被丰富,土壤湿度大,裸地少,并且流域内南北地表特征变化显著,北部山区以自然地表为主,南部平原以建设用地人工地表为主。南北地表类型差异在NDVI-Albedo空间中表现直观,利用NDVI-Albedo作为指示因子,在流域内的山区平原衔接部位设置13条样带,结合小波分析的方法,将后溪流域南北划分,确定出一条长12.26 km的地表分界线。此分界线代表南北不同地表类型,反映不同的城镇化水平与人类活动强度,为流域因地制宜分区管理提供了基础数据与依据。     

京杭大运河无锡段水质和土地利用的响应关系

以京杭大运河无锡段2003年7月和12月两景SPOT-5正射影像为数据源,结合断面水质数据,利用基于最小二乘法的多元回归方法,建立了枯水期和丰水期水质参数与土地利用的响应模型。结果表明:以监测断面为中心的缓冲区距离的空间变化与水质监测指标之间有很明显的响应关系,建立的模型显示,丰水期DO、CODMn、BOD5、TN和TP的最大响应宽度分别为100、100、300、200和100 m,枯水期的最大响应宽度则为500、200、300、400和200 m。运河的水质污染主要受离河岸较近的土地利用结构的影响,耕地上产生的农业污水、商业和工业中的废水以及大面积裸地上居民生活垃圾和建筑垃圾产生的污水是导致京杭大运河无锡段水质恶化的重要原因。     

微米级空间碎片撞击太阳电池研究

目的评估航天器太阳电池阵遭遇微米级空间碎片撞击后性能的下降程度。方法利用激光驱动飞片发射系统针对硅太阳电池开展系统的试验工作,对太阳电池机械损伤特性及伏安特性进行测试。利用ORDEM2000软件计算航天器所在轨道的碎片通量和速度。结合试验结果,计算航天器太阳电池阵因微米级空间碎片撞击引起的最大输出功率衰减率。结果太阳电池最大输出功率衰减率与溅射区直径呈二次函数关系,与表面污染率近似相等。未来5年天宫一号所在轨道航天器太阳电池因微米级空间碎片撞击引起的最大输出功率衰减率为0.45%。结论利用该研究结果可以预计航天器太阳电池因微米级空间碎片撞击引起的最大输出功率衰减率,为航天器总体设计提供技术支持。     

喀斯特地区城市绿地土壤呼吸对降水变化的响应研究

降水是影响土壤呼吸一个重要的影响因子,研究降水对土壤呼吸的影响,对估计和预测陆地生态系统土壤呼吸变化有着重要的意义,但目前自然降水对喀斯特地区城市绿地土壤呼吸影响的研究目前还鲜有报道.本研究利用静态暗箱法,对降水后贵阳城市绿地土壤呼吸速率变化进行了24 h定位监测,对比研究了不同强度降水后土壤呼吸速率变化,并分析了水热...     

气象条件对可吸入颗粒物浓度的影响

气象条件对可吸入颗粒物浓度有较大的影响,通过对鞍山市二年来的监测数据进行分析,得出了结论并提出建议.     

丙酮、异丙醇的分离和顶空气相色谱测定

研究了环境大气及水质中丙酮和异丙醇的分析方法，采用顶空气相色谱法测定，用ＰＥＧ－２０Ｍ３０ｍ＊５３ｕｍ和ＦＦＡＰ３０ｍ＊５３０ｕｍ大口径弹性石英毛细管柱分离，氢火争离子化检测器检测，避免了复杂的基体干扰，得到了良好的分离效果和较高的灵敏度，丙酮和异丙醇检出限最低分别＝可达０．０３ｍｇ／Ｌ、０．０４ｍｇ／Ｌ，０．００２ｍｇ／ｍ＾３、０．００３ｍｇ／ｍ＾３。     

光电测量技术在狭小空间电场测量中的应用

电磁场测量的精确度是电磁兼容测试重要的指标。传统的电场测量,使用了金属结构的天线以及金属电缆,这些都不可避免给测量系统引入干扰,造成被测场的扰动。这一点对于小空间内电磁环境测量尤为显著,因此,需要引进对被测场扰动小的光电测量技术。论述了光电测量技术和测量设备在电磁兼容领域的发展,并阐述了在狭小空间内开展光电测量遇到的难题。     

The prenatal detection of a familial pericentric inversion of chromosome 19

A familial pericentric inversion of chromosome 19 was detected prenatally in a young primagravida. As far as the authors are aware there are no previous published reports of this rare abnormality being ascertained in this manner. The problems of counselling such a family are considered.